Two-stroke loop-scavenged engine and method of firing same



Sept. 11, 1956 J. E. cANd sE 2,762,351

TWO-STROKE LOOP-SCAVENGED ,ENGINE -AND METHOD OF FIRING SAME Filed Jan. 31, .1952 4 Sheets- Sheet 1 IN VEN TOR.

BY w M.

ATTORNEYS Sept. 11, 1956 .1. E. CANOOSE 2,762,351

TWO-STROKE LdOP-SCAVENGED ENGINE AND METHOD OF FIRING SAME Filed Jan. 31, 1952 4 snee ts-sheet 2 Septgll, 1956 E, CANQQSE,

TWO-STROKE LOOP-SCAVENGED ENGINE AND METHOD OF FIRING SAME Filed Jan. 51, 1952 4 Sheets.Sheet 3 :xmewr P0575 0PM 5x5: Pain dare ZNVENTOR. BY cf/r [/Ww/ ATTORNEYS TWO-STROKE LOOP-SCAVENGED ENGINE AND METHOD OF FIRING SAME Filed Jan. 51, 1952 Sept. 11, 1956 J. E. cANoosE 4 Sheets-Sheet 4 V EN TOR.

A T TORNEYS United States Patent TWO-STROKE LOOP-SCAVENGED ENGINE AND NETHOD 0F FIRING SAME John E. Canoose, Cleveland, Ohio, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Application January 31, 1952, Serial No. 269,261

Claims. (Cl. 123 69) This invention relates to internal combustion engines and particularly to such engines of the two-stroke loopscavenged type operating on gas fuel and electric spark ignition.

Engines of this type have heretofore been proposed in which a major part of the combustion chamber is defined by the directly opposing surfaces of the cylinder head and the piston, and a minor part or extension of the combustion chamber is recessed within the cylinder head well. Also it has been known in such designs to introduce the gas fuel directly into the combustion chamher and to locate the spark plug in such minor part, whereby the initial burning of the fuel charge will take place in the minor combustion chamber part and the subsequent development of the flamefron t-to the limits of the major part of the chamber may be better directed and timed. The present invention accomplishes this gencral result in a novel manner having numerous advantages over prior art structures, the most important of which include the following: 1) stratification is obtained of the gas-air mixture within the combustion chamber, with resultant regularity of engine firing and freedom from detonation, even at overload, and 2) the size of the minor combustion chamber part may be changed without the necessity of altering the basic or fixed dimensions of the engine cylinder unit.

The means by which these and other advantages are obtained in accordance with the inventionv will be clearly understood from the following description in which reference is made to the drawings, wherein:

Figure 1 is a view ofone cylinder-unit of a two stroke loop-scavenged internal combustion engine embodying the principles of my invention, with parts broken away and in section, and showing the piston at the bottom dead center position. r

Figures 2-5 are fragmentary views similar to Figure l but showing the piston at successively higher positions in the cylinder, "the piston being at the top dead center position in Figure 5. a V

Figure 6 shows a representative timing diagram of the opening and closing of the cylinder air inlet andexhaust port and the gas valve during an engine rotating'cycle for one cylinder unit.

Figure 7 is a longitudinal sectional view of the head end of the cylinder unit taken on line 7'7 of Figure 1, except with the piston shown at the upper end of its stroke as in Figure 5.

Figure 8 iso longitudinal sectional view of theplug member of Figure 7, the section being taken at-right angles to that of Figure 7.

' Figure 9 is a fragmentary sectional view similar to Figure 7 but taken a-t-an angle to the plane thereof to show the manner of securing "the plug member to the cylinder head.

Referring now to the drawings, and firstly to Figures 1 and 7, the numeral 2 designates generally asingle cylinder unit of 'an internal combustion engine including a cylinder 4 closed at its upper end by a cylinder head 6;

and interconnecting the ice In the particular unit shown the cylinder and head are integral with each other and have a common coolant jacket space 8, best shown in Figure 7, which surrounds the inner wall-s 10 of the cylinder and 12 of the head portion. The bore of the cylinder has a liner 16 in which is slidably fitted the piston 18. Two or more openings as at 20 are provided through which coolant may be introduced to and returned from the jacket space 8.

As shown in Figure 1, on generally diametrically op= posite sides of the cylinder unit 2 there are provided one or more air inlet ports 22 and exhaust ports 24 which are controlled by the piston 18 in the usual manner for loop-scavenged, two-cycle engines, wherein when the piston is at the bottom dead center position of Figure 1 both the inlet and exhaust ports are fully open and air flow-s into and across the cylinder. As shown, :both the inlet and exhaust ports 22 and 24 are inclined to the cylinder axis to promote the looped or U-shaped path of the scavenging air (indicated by arrows). Mounted in the cylinder head 6, on the inlet port side of the cylinder unit, is a suitable gas inlet valve means which in the form shown comprises a poppet type valve 26 arranged for vertical reciprocation in a stationary valve housing 28 through which gas fuel is periodically conducted into the interior of the cylinder from a suitable source (not shown). 29 is a test plug and does not concern the present invention Figure 6 shows --a representative timing diagram of the relative opening and closing of the inlet port 22, exhaust port 24 and gas valve 26. j The head end or crown 30 of the piston 18 has a central protuberance 32 surrounded by an annular con-, cavity'34, the outer extremities of which are rimmed by a conically tapered surface 36 extending inwardly and upwardly from the cylindrical outer periphery 38 of the piston. The cylinder head inner. wall 12 has its inner surface provided with a, conically tapered portion 40 facing the conically tapered piston surface 36 and a relatively flat portion 42 disposed opposite the concavity 34 in the piston crown. When the piston is in its top dead center position (Figures 5 and 7)the major part 44 of the combustion chamber for the cylinder unit 2 is thus defined by the opposing surfaces 34, 36 of the piston and '40, 42 of the cylinder head wall 12, 1

Approximately opposite the bottom of the" concavity 34 the cylinder head inner wall 12 turns upwardly (away from the piston crown 30) to merge with a wall 45 forming a passage 46 whose lower end 48 is in direct communication with the combustion chamber part 44; Passage 46 extends through the cylinder head as shown, the 'wall 45 forming this passage being continuous with cylinder head inner and outer walls 12 and 52. Coolant circulated through the jacket space Sthus flows around the passage 46 andefiects, the necessary cooling of the passage inner wall'surface 54; -Removably secured to the cylinder head 6'is a plug ing into the passage 46, and

peripheral surface 64 of the shank portion '58 is in close" fitting engagement with the inner wall surface 54 of the passage 46 and is preferably provided with one or more grooves 66, in each of which is located an outwardly expandable. packing 68 to insure a gas tight seal with the surface 54. The shank portion 58 terminates just belowthis packing with an end face 70 which closes the passage at a predetermined height above the main combustion chamber surface 42. The interior of the cupshaped shank portion constitutes a well 72 which terminates at its lower end in a threaded opening 74. Seated on a shoulder 76 at the bottom of the well 72 and threadedly engaging the opening 74 is a spark plug 78.

Thus it will be seen that the portion of the passage 46 below the plug member 56 provides a minor part 44' of the combustion chamber of the cylinder unit 2 within the cylinder head, and that while the transverse dimension of the passage is a fixed value, the height of the shank end 70 above the main internal wall surface 42 of the cylinder head (and consequently the volume of this minor part of the combustion chamber) may be made larger or smaller in relation to the total volume of the combustion chamber by substituting a plug member having a longer or shorter shank portion 58.

Cooling of the shank end 70 is provided by forming the side walls of the shank portion with an internal U- shaped cored chamber 80 which extends substantially the full length of the shank portion 58 and has its lower ends interconnected by a cored passage 82. The uncored wall portion 84 between the two arms of the U-shaped chamber 89 has a longitudinally drilled passage 86 terminating at its lower end in communicating with the cored connecting passage 82 and closed at its upper end by a pipe plug 88. Additional drilled passages 90, 92, 94 and 96 in the flange portion connect the upper ends of the drilled passage 86 and cored chamber 80 respectively with passages 100 and 102 extending through the cylinder head upper wall 52 into communication with the cylinder and head jacket space 8.

The above described working cylinder assembly operates on the conventional, loop-scavenged, two-stroke cycle, but the method used for mixing fuel gas with the air for combustion dilfers basically from the usual meth od. The fuel/air ratio of that portion of the charge compressed into the minor part 44 of the combustion chamber, in which is located the spark plug, is higher than the fuel/air ratio of that portion of the charge which is compressed in the main combustion chamber 44. When high compression ratios are used to produce efficient combustion while developing only moderate mean effective pressures, and while using quantities of combustion air normal for this type engine, and when burning natural gas, the volume of naturalgas required is so low that the mean fuel/air ratio is too low to properly propagate flame during the combustion period. Heretofore, various schemes have been used to improve this condition when igniting by electric spark such as:

(a) Igniting the charge at more than one point in the combustion chamber.

(b) Producing high turbulence in the charge before the charge is ignited.

(c) stratifying the fuel/ air charge, so as to provide a rich mixture in one portion of a combustion chamber of conventional shape, so that, when ignited, the flame will propagate through this rich mixture part of the combustion charge.

In accordance with the present invention the unusual shape of the minor combustion chamber part 44 and its relative position with respect to the gas valve 26 and the air inlet and exhaust ports 22 and 24, respectively, comblue to provide a novel method and means for controlling the degree of Stratification of the fuel/ air charge. The design of the minor combustion chamber part 44' limits the straight line length of flame travel path within the rich fuel/air stratum. Long flame travel paths-in uncontrolled stratified mixtures may cause the high detonating pressures which are experienced when fuel/ air mixtures are ignited in such cylinders which do not incorporate the minor chamber part 44'.

The herein disclosed method used for isolating a stratified rich mixture in the combustion chamber part 44', fitted with a spark plug, and of such shape as to limit flame travel that satisfactory combustion pressures can be obtained in large cylinders, will now be described. The gas valve 26 is located on the scavenging air inlet side of the cylinder head, as distinguished from being cated in the side of the cylinder as is the case with prior art engines of this type. The scavenging air flowing up and across the cylinder in the general manner, as shown by the arrows sin Figure l, meets the gas, indicated by the arrows g in Figures 2 and 3, flowing into the cylinder through the gas valve 26, and carries the gas upward and acrossthe cylinder toward the exhaust side of the cylinder. This loop air flow movement persists after the inlet and exhaust ports have been closed.

' As shown by the timing diagram in Figure 6, the gas valve opens before the intake ports close. The incoming gas, flowing out over the conical head of the valve 26 impinges in umbrella form, as shown in Figure 2, against the scavenging air flowing across the top of the cylinder. This causes the body of gas to move to the right and under the minor part 44' of the combustion chamber. After the piston 18 passes the upper edge of the exhaust ports 24, as shown in Figure 3, compression begins; and some of the intake air, mixed with the gas from the valve 26, starts flowing into the chamber part 44' due to compression. Gas continues to flow from the valve 26 until the piston reaches the gas valve closing point shown by Figure 4. During the period of time required for the piston to move from the position of Figure 3 to that of Figure 4 the gas from valve 26 flowing directly under the chamber part 44' is forced by rising air directly into the chamber part 44', and the gas flowing in other directions from the valve 26 mixes with the scavenging air generally in the left or air inlet port side of the main part 44 of the combustion'chamber. Some of this gas, in flowing toward the right or exhaust port side of the cylinder with the scavenging air, after closure of the exhaust ports, passes directly under the combustion chamber part 44'. This enriched mixture is forced by the compressing action of the piston to flow upward into the chamber part 44. In this manner the chamber part 44' receives its charge from the gas-rich mixture around the gas valve 26. Thus, with the gas valve located in the scavenging port side of the cylinder, and with the timing as above described, the mixture which enters the chamber part 44' after compression starts, and while the gas valve is open, will be richer in fuel than the average of the mixture which exists in the main combustion chamber 44.

During the period of time for the piston to move from the position of Figure 4 to that of Figure 5 (top dead center) the piston will force part of the mixture remaining in the cylinder, above the piston, into the chamber part 44'. Summarizing, the final charge in the minor chamber part 44, when the piston reaches top center, is made up of three distinct parts:

(a) The scavenging air within the cylinder as shown in Figure 1. If a compression ratio of 12:1 is assumed,

- the volume of this scavenge charge will be 5 of that of the final charge or 8%.

(b) In moving from the position of exhaust port closure to gas valve closure, the piston moves through about /3 of its compressing stroke, i. e., the piston stroke past exhaust port closing. The volume of rich mixture entering the minor combustion chamber part 44' during this period, therefore, will be /3 of the final charge.

(c) The remainder of the charge in the minor chamber part 44' will be made up from the mixture remaining in the working cylinder at the time of gas valve closure.

With the arrangement above described the engine fires regularly and carries overloads without detonation; whereas with the same compression ratio, and with other things unchanged, except arrangements where the minor com- 7 bustion chamber part 44 has been eliminated, or, its effeet minimized by placing the gas inlet valve in the side of the cylinder head opposite to the scavenging air inlet ports, it has been found impossible to operate continuously at rated load and without usual detonations.

When using the above described combustion chamber two principal effects are realized, both of which act to limit detonation.

('a-) The maximum length of flame travel path Within the minor combustion chamber-part 44' is short, -since the chamber part 44 is small with relation to the size of the working cylinder, as shown in Figure 5 (b) The mean mixture ratio in the main part 44o'f the combustion chamberis very lean, so that flame progagation cannot progress in the usual accepted -sense. Combustion within this main of the combustion chamber is dependent on the violent turbulenceset up by the rapid combustion of the rich mixture in the minor part 44' of the combustion'chamber.

While a specific structural embodiment of theinvention has been shown and described, it will be appreciated that various minor alterations and changes may be made therein without departing from the spirit and scope of the invention as hereinafter claimed. For example, an oil fuel injector or other means for igniting the .stratified ,gas/ air mixture -in the minor'chamber 44' could be substituted for the spark plug 78.

I claim:

1. In a cylinder unit for an internal combustion engine, a cylinder,-a piston in the cylinder having a crown portion with a central upstanding protuberance surrounded by an annular concavity, acylinder head on said cylinder having an inner wall opposing and cooperating with said piston crown portion to define a first "combustion chamber, said inner wall including an annular generally fiat portion disposed opposite said concavity and having a greater inner diameter than the inner diameter of said concavity, said cylinder 'head ha'ving an outer wall spaced from said inner Wall, said inner and outer walls having 'an interconnecting wall dfinin'g a passage 'through the cylinder head, said passage having one end open to said first-cornbustit rn chamber at said inner diameter of said annular generally -flat portion and providing unobstructed communication between 'said 'fir'st "combustion chamber 'and the interior of said I'pass'a'ge, a removable plug extending into the opposite end of said passage and secured to said outer wall, said plug being generally cup-shapedwiththe closed-end of the cup disposed inwar'dly of the .passage and provided with anaper- =ture, a spark plug mounted :in said aperture, said spark :plug and closed end of said :r'emovable rp'lug being spaced from said cylinder head inner wall and forming a second combustion chamber with said interconnecting wall.

2. A loop-scavenged internal combustion engine having a cylinder closed at one end by a cylinder head defining a combustion chamber of which a relatively small part is in the form of a recess in said head closed end of the cylinder, means for introducing and directing scavenging air into one side of the cylinder for flow transversely and upwardly thereof against the cylinder head while simultaneously permitting the escape of combustion gases and scavenging air through the opposite side of the cylinder, means for introducing gaseous fuel into the path of the upper portion of the transversely moving air for intermixture in greater concentration with said portion than with the remainder of said air and movement with said upper portion across the upper end of the cylinder toward and into the cylinder head recess, means for compressing the gaseous fuel and air mixture against the cylinder head, and means for igniting the portion of the compressed mixture disposed in the cylinder head recess.

3. A loop-scavenged internal combustion engine having a cylinder closed at one end by a cylinder head defining a combustion chamber of which a relatively small part is in the form of a recess in said head closed end, means for introducing and directing scavenging air into one side of the cylinder for flow transversely and upwardly thereof against the cylinder head while simultaneously permitting the escape of combustion gases and scavenging air through the opposite side of the cylinder; means for simultaneously introducing gaseous fuel into the path of the transversely moving air adjacent the cylinand means including a valve and an o der head for intermixture and movement therewith in a relativlyrich fueT/ air mixture stratum vacross the upper end .of the cylinder and into the cylinder head recess; means for sequentially discontinuing said air inflow, then discontinuing said combustion gas escape, and finally compressing a portion of said stratum within said recess and the remainder of said gaseous fuel and air mixture against the cylinder head, and tnans .for electrically igniting the portion of the compressed mixture disposed in the cylinder vhead recess.

4. An internal combustion engine having a cylinder with a cy'linderhead at one end defining a two-part combustion chamber wherein one of said par tsis .in the form of a recess 'in the cylinder facing surface of the cylin'c'le'r head, means for creating a Stratified rtiix'turefof natural gas and air in said two-part chamber including means for introducing and directing scavenging air into the cylinder from one side thereof (for movement upwardly therein against and across ihe cylinder head transversely of the recess, means for simultaneously introducing natural gas into the upwardly and transversely Zflowing air 'between said side and said recess 'at a veraci y relative to the air flow velocity such that intermixture of said natural gas and air is predominately confined to the upper portion of the cylinder for flow as 'a rich mixture into said recess, leaving the remainder of said airless richly charged with natural=gas, means for simultaneously permitting the escape of combustion ases from the :cylinder in advance of the air front crea ed by said air inflow, means for terminating said air rrrfletv and coinbustion gas escape and intially cernpressing the natural gas and air against the cylinder head while continuing said natural gas inflow, aniifireans for terminating said natural gas inflow while "furtherconipressing the natural gas and air against the cylinder head. p

'5. In a two-cycle internaljcorribust'ion engine, a cylinderhavin'g oppositely disposed side airinle't and exhaust .ports arranged for loop caven'g'ing of the cylinder, is cylinderheadhaving a mixture stratification recess open to the interior of the cylinder, 'a p ston re'ciprocable in the cylinder, said piston and Cylinder head "forming a main combustion chamber opposite the recess opening,

' ing eon reuse "thereby for -introducing gasedu's fuel into {said .ihain fc'ombustion chamber during the scavenging of the cylinder, said opening being located in the path of the scavenging air entering said recess and cooperating with said valve when open to direct the gaseous fuel into said main combustion chamber for relatively rich intermixture with said last named air and relatively lean intermixture with the remainder of the scavenging air.

6. In a two-cycle internal combustion engine having a loop-scavenged working cylinder terminating in a cylinder head transverse wall, said wall having a mixture stratification recess spaced from the air inlet side of the cylinder, a valved opening in said wall through which gaseous fuel is adapted to be introduced for intermixture and movement with the scavenging air flowing toward said recess, and a valve controlling said opening, said opening cooperating with the valve to direct said gaseous fuel for relatively rich and lean intermixture with the strata of air respectively most adjacent and remote from said transverse wall.

7. In a loop-scavenged internal combustion engine working cylinder unit including a cylinder, a piston, and a cylinder head, said cylinder having a scavenging air inlet port in one side thereof closable by the piston at a, predetermined time during the movement of the piston .toward the cylinder head and an oppositely disposed exhaust port closable by the piston after a further predetermined movement of the piston toward the cylinder head, said piston having a crown cooperating with the walls defining said ports and the piston opposed wall of the cylinder head to direct the scavenging air flow upwardly against the cylinder head along said one side of t 7 t the cylinder and thence transversely of the cylinder, said piston opposed wall of the cylinder head having'a mixture stratification recess in the path of the scavenge air flowing across the cylinder, means including a valve controlled gas fuel supply port in said cylinder head wall on the scavenging air inlet port side of the cylinder from said recess whereby gas may be introduced for intermixture and movement with said air, a valve closable on said port, said portcooperating with the valve when open and with the transversely moving air to induce a relatively rich mixture with the relatively upper stratum air which scavenges said recess and a relatively lean mixture with the relatively lower stratum of air scavenging the remainder of the cylinder, and a spark plug'is said recess for igniting the gas/air mixture compressed therein by the 'piston'after closure of said exhaust port' 8. A two-stroke internal combustion engine comprising, a cylinder, rn'eansfor introducing and directing'air into one side of the cylinder for flow first toward one end of the cylinder and thence transversely across said end of the cylinder, means for simultaneously introducing gas fuel into said end of the cylinder at a velocity relative to the air flow velocity to provide a relatively rich intermixture and movement with the portion of the transversely flowing air adjacent said end, means for cornprmsing said portion of said gas and air mixture and simultaneously compressing the remainder of the gas and air mixture in said end of the cylinder below said portion, and means for electrically igniting said portion of the gas and air mixture.

9. An internal combustion engine comprising a cylinder, means for moving a column of air into the cylinder upwardly along one side of the cylinder and across the upper end of the cylinder, means for simultaneously introducting gas fuel into said cylinder end at a velocity relative to air velocity such that the gas mixes in relatively rich concentration with the upper portion and in relatively lean concentration with the remaining lower portion of said air as it moves across said end of said cylinder, means for compressing both said relatively rich and lean mixed portions in said cylinder, and means for igniting said relatively rich portion and allowing its combustion to propagate a flame to sequentially ignite said relatively lean portion.

r 10. In an internal combustion engine a cylinder hav-- ing a piston and a head, said piston and head having opposed wall surfaces defining a'major combustion chantber part when the piston is at the head end of its stroke, said head having a passage extendingcentrally from its piston opposed surface, a plug in said passage removably secured to said head, said plug and the walls of said passage between the plug and said last named surface de fining a minor combustion chamber part having approxi mately one-sixth the volume of said major part and unobstructed communication therewith, said cylinder having' an upwardly inclined'air inlet port in one side wall and a similarly inclined exhaust port in its opposite side well, said portsbeing open when the piston is at the opposite end of its stroke for the scavenging and charging of the cylinder and said combustion chamber parts, a gas fuel admission valve insaid head on the side of 'said passage nearest said air inlet port, and a spark plug in said minor combustion chamber part.

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